The present invention advances the art of disposable diapers that have a reinforced fastening area, i.e., an area of the diaper to which an adhesive tape is pressed and adhered to fasten the diaper around an infant or other person wearing the diaper. The fastening area generally lies along one side edge of the generally rectangular diaper, and lies on the outer liquid-impermeable film of the diaper, which in commercial disposable diapers is typically a thin film of polyethylene. The thinness of the polyethylene is desirable for several reasons, but when adhesive tape is adhered to it to fasten the diaper, or when the tape is removed to reposition the diaper or to check its condition, forces are applied that can tear the polyethylene and thus destroy the usefulness of the diaper.
The prior art has taught various techniques for reinforcing the outer impermeable film of the diaper. One technique involves coating the film with a reinforcing material either on the inner or outer surface of the film. See U.S. Pat. No. 4,296,750 (the interior surface of the outer impermeable film is coated with a hot-melt adhesive layer which has both a Ring and Ball softening point lower than that of the film and a modulus of elasticity lower than that of the film) or U.S. Pat. No. 4,210,144 (a hot-melt adhesive having high tensile strength and a low elongation to tensile force property relative to the outer impermeable film is applied on the outer impermeable film in a predetermined pattern, e.g., as an array of parallel stripes, preferably on the inner surface of the film to both bond the film to the absorbent pad of the diaper and to reinforce the film). Problems with this technique include the facts that the cohesive strength of the coating can be too low to allow lasting and complete holding of an adhesive tape pressed against it; some coating materials taught in the patents have a high softening point that can lead to deformation of polyethylene during coating; and patterned coatings can lead to nonuniform reinforcement.
A different technique of reinforcement involves adhering a plastic strip to the fastening area of the diaper. Teachings in the literature about this technique include U.S. Pat. No. 3,867,940 (a scrim or plastic film is bonded to the impermeable film "by known methods" or, if a polyethylene gauze is used, by heat and pressure); European Patent Application No. 0,080,647, published June 8, 1983 (a plastic strip such as a smooth-surfaced polypropylene strip is adhered to the impermeable film by a "layer of adhesive"); and German Offenlegungsschrift No. 33 38 201 A 1, laid open April 26, 1984 (a plastic strip of preferably polyethylene or polypropylene or polyester is "firmly adhered" to the impermeable film).
In commercial practice, the plastic strip of this technique has been adhered to the outer impermeable film with a pressure-sensitive adhesive. While offering convenient adhesion, the use of pressure-sensitive adhesives has a number of disadvantages. For example, to allow a uniform low-force unwinding of the adhesive-coated plastic reinforcing strip from a storage roll, the top surface of the reinforcing strip, i.e., the surface which becomes the target area to which the fastening tape is adhered in fastening the diaper around an infant, is typically covered with a low-adhesion backsize (LAB), thereby minimizing adhesion between the adhesive layer and that top surface. But the minimizing of adhesion to the target area where the fastening tape is to be adhered is exactly contrary to an intended characteristic of the target area, i.e., the characteristic of providing a surface to which the fastening tape can become reliably and lastingly adhered. An LAB could be avoided by covering the pressure-sensitive adhesive surface with a release liner, but such a liner adds undesired cost.